1. Field of the Invention
The present invention relates to a gate driver circuit. More particularly, the present invention relates to a gate driver circuit for eliminating residual image from a display device.
2. Description of the Related Art
FIG. 1 is a driving timing sequence diagram for a thin film transistor (TFT) liquid crystal display (LCD) device. As shown in FIG. 1, the conventional TFT LCD includes a display panel and a back light module. At present, the internal start-up sequence for the TFT LCD includes switching on the main power source (as shown in curve A) of the TFT LCD through the time sequence tN1. This includes applying a voltage to the common electrode of the TFT LCD and the pixel electrode. Then, in time sequence tN2, image signal (as shown in curve B) is input to the pixel structure of the TFT LCD. Next, in time sequence tN3, the back light module is turned on (as shown in curve C) to provide the display panel with a light source and display an image on the TFT LCD. Furthermore, as shown in FIG. 1, the internal shut down sequence of the conventional TFT LCD includes a sequence of steps, which is simply the reverse of the start-up sequence. First, in the time sequence tF1, the back light module is shut down, and then the image signal fed into the pixel structure terminates in the time sequence tF2. After that, the main power source of the TFT LCD is turned off in the time sequence tF3.
Accordingly, some time after shutting down the back light module but before terminating the image signal, that is, in the time interval between tF1, to tF2 (typically, about 16.7 msec), the image signal still exists within the pixel structure and residual electric charges still exist on the pixel electrode. These residual charges do not have an effective exit path so that they can only be dissipated after the passage of a period. Therefore, a residual image frequently still persists on the TFT LCD for a while onward from the time sequence tF3 after turning off.
FIG. 2 shows a conventional gate circuit for driving a display device. FIG. 3 is a timing diagram showing the conventional power-off logic-driving sequence of a display device. As shown in FIGS. 2 and 3, when the power source of the display device is on, the inductor 201, the capacitors 203, 205 together with the integrated regulator circuit 207 in FIG. 2 provide the source power (VDD) necessary for driving the logic circuit of the display device. Meanwhile, according to the logic state (VDD or VSS) of the logic circuit of the display device and through the level shifter of channel circuits in the gate driver, the gate logic-driving source (VGH, VGL) converts the logic state (VDD or VSS) into a gate logic-driving source (VGH or VGL) for turning on or shutting down the thin film transistor in the pixel structure within the display device.
Then, when the display device is shut down (shown by the dash line I in FIG. 3), the shutting down of the logic-driving source (VDD) and the gate logic-driving source (VGH, VGL) are unanimous. Thus, after shutting down the display device, the gate logic-driving source (VGH, VGL) still has some residual electric charges to turn on or off the thin film transistors of the pixel structures inside the display device and produce a residual image.
To resolve aforesaid problem, three controlling integrated circuits (IC) together with a microprocessor are conventionally used after the timing sequence tF3 for controlling the shut-down timing sequence of the driving sources (VDD, VGH, VGL) required by the logic circuit of the display device. Thus, when the display device is shut down, the shutting sequence of the logic-driving source (VDD) is extended so that all the thin film transistors of the pixel structures inside the display device remain on, allowing the pixel electrode to discharge rapidly and eliminate any residual image.
However, because the conventional method demands the deployment of three additional controlling ICs and a microprocessor for controlling the shutdown timing sequence of the driving sources (VDD, VGH, VGL) in the logic circuit of the display device, the production cost is increased considerably.